In cellular networks, HSDPA (High-Speed Downlink Packet Access) systems are continuously developing to improve performance. The development includes several features in both UL (Uplink) and DL (Downlink) to enhance system performance and capacity as well as enabling a better user experience. Examples of developments are downlink MIMO (Multiple Input Multiple Output) (3GPP TR (Third Generation Partnership Project Technical Report) 25.872 Release 7) and dual cell/dual band HSDPA (3GPP TR 25.872 Release 8 & 9). There is also work going on to specify Multi-flow HSDPA (MF-HSDPA) Data Transmission for 3GPP TR 25.872 Release 11.
The concept of MF-HSDPA is to allow UEs (User Equipment nodes, also referred to as mobile/wireless terminals) to receive HSDPA data from two separate cells. The cells can belong to the same Node B (intra site MF-HSDPA) or to different Node Bs (inter site MF-HSDPA). In the former case, the solution is similar to DC-HSDPA (Dual Cell HSDPA, also known as Dual Carrier HSDPA), but on the same frequency, with a data split in the MAC-ehs (Media Access Control—enhanced high speed) layer. In the inter site case, the split may be in either the PDCP (Packet Data Convergence Protocol) or RLC (Radio Link Control) layer.
A potential benefit of introducing MF-HSDPA is that cell edge users may suffer from bad coverage and/or low throughput which brings down the overall system capacity. If these users could use available resources from neighbouring cells, i.e. receive data also from the non-serving cell, their situation could be significantly improved. This would improve the overall system capacity and the user performance for cell edge users.
HSDPA is described in further detail in HSDPA Multipoint Transmission, 3GPP TR 25.872.
When RLC transmissions get stuck on one link, it may be a good alternative to retransmit the RLC PDU(s) (Protocol Data Unit(s)) over the other link. If the retransmission cannot get through over the other link either, further retransmissions could be switched back to the original link. However, in this case there could be old copies existing at the link(s) besides the last retransmitted copy. Duplicate copies can result in lower application level throughputs.